1. Field of the Disclosure
The present disclosure is applicable to any type of automatic transmission (for example, a continuously variable transmission, a multi-range transmission, an automatic manual transmission, which is a manual transmission that involves the use of automatic gear shifts, etc.). More specifically, the present disclosure relates to a shifting oil-pressure control apparatus for an automatic transmission which may provide improved controllability and responsiveness of a shifting oil pressure when a selection operation for switching between a driving range and a non-driving range is performed by a driver.
2. Description of the Related Art
In an automatic transmission, a park (P) range, a reverse (R) range, a neutral (N) range, a forward automatic gear-shift (D) range, etc., which designate gear-shift modes, are arranged in that order. When a selection operation for manually switching between the above-mentioned ranges is performed, a manual valve is operated in response to the selection operation. More specifically, the manual valve is moved to a position corresponding to the selected range, thereby setting a gear-shift mode that corresponds to the selected range.
As described in, for example, Japanese Unexamined Patent Application Publication No. 2004-197758, the manual valve is operated in response to the selection operation for switching between the ranges in the following manner. That is, a shift lever used by the driver to select one of the ranges is mechanically connected to the manual valve with a link mechanism, a wire, etc., and the manual valve is operated in response to the selection operation by the mechanical means.
In addition, as described in Japanese Unexamined Patent Application Publication No. 2004-197758, because the above-mentioned ranges are successively arranged, the manual valve has a reverse (R) range position, which is a driving range position, and a forward automatic gear-shift (D) range position, which is another driving range position, at one and the other side of a neutral (N) range position, which is a non-driving range position. At the neutral (N) range position, a reverse shifting hydraulic circuit for a reverse shifting friction element, which is to be set to an engaged state when a selection operation for switching from the neutral (N) range to the reverse (R) range is performed, is disconnected from a line pressure circuit and is connected to a drain port. In addition, a forward shifting hydraulic circuit for a forward shifting friction element, which is to be set to an engaged state when a selection operation for switching from the neutral (N) range to the forward automatic gear-shift (D) range is performed, is also disconnected from the line pressure circuit and connected to a drain port. Accordingly, the reverse shifting friction element and the forward shifting friction element are set to a disengaged state and the automatic transmission is set to a state in which power cannot be transmitted (neutral state).
At the reverse (R) range position or the forward automatic gear-shift (D) range position, the reverse shifting hydraulic circuit for the reverse shifting friction element or the forward shifting hydraulic circuit for the forward shifting friction element is disconnected from the drain port and is connected to the line pressure circuit. Accordingly, the reverse shifting friction element or the forward shifting friction element is set to an engaged state by a line pressure and the automatic transmission is set to a state in which reverse rotational power or forward rotational power can be transmitted.
In the case where the manual valve having the above-described structure is mechanically operated in response to the selection operation, as described in Japanese Unexamined Patent Application Publication No. 2004-197758, the following procedure is performed. That is, when a selection operation for switching from the reverse (R) range or the forward automatic gear-shift (D) range to the neutral (N) range is performed, the reverse shifting friction element or the forward shifting friction element, which has been in the engaged state, is disengaged to set the automatic transmission to the neutral state. At this time, a flow-rate regulator, such as an orifice, is often provided in the drain port for draining the shifting hydraulic circuit for the corresponding shifting friction element, so that the engagement-pressure reduction rate of the corresponding shifting friction element can be adjusted.
However, when the engagement-pressure reduction rate of the shifting friction element is adjusted by regulating the flow rate with the orifice or the like, the engagement-pressure reduction rate of the shifting friction element is exclusively determined by the degree of flow-rate regulation provided by the orifice. Accordingly, the engagement-pressure reduction rate cannot be actively controlled.
When the above-described R→N selection operation or D→N selection operation is performed, the engagement pressure of the corresponding shifting friction element is preferably eliminated as soon as possible without causing a problem of disengagement shock (R→N selection shock or D→N selection shock). An engagement-pressure reduction rate and an engagement-pressure reduction pattern for achieving this differ depending on the driving conditions. If the engagement-pressure reduction rate of the shifting friction element is exclusively determined by the degree of flow-rate regulation performed by the orifice or the like, the demand regarding the selection shock and the demand regarding the selection response, which conflict each other, cannot be satisfied at the same time in a well-balanced manner.
In addition, in an R→N→D selection operation in which the range is switched to the D range immediately after the R→N selection operation or in a D→N→R selection operation in which the range is switched to the R range immediately after the selection operation, the following problems occur in addition to the above-described problems.
That is, when the manual valve is mechanically moved to the D range position or the R range position in response to the N→D selection operation or the N→R selection operation, the manual valve causes the line pressure to be directly applied to the forward shifting friction element or the reverse shifting friction element to set the forward shifting friction element or the reverse shifting friction element to the engaged state. Therefore, the forward shifting friction element or the reverse shifting friction element is too quickly set to the engaged state and there is a risk that an engagement shock (selection shock) will occur.
Therefore, as described in Japanese Unexamined Patent Application Publication No. 2004-197758, a flow-rate regulator, such as an orifice, is often provided in the shifting hydraulic circuit for each shifting friction element, so that the shifting oil pressure increase rate (rate at which the engagement of the corresponding shifting friction element progresses) can be adjusted.
The rate at which the engagement of the corresponding shifting friction element progresses (selection response) is preferably set as high as possible without causing an engagement shock (selection shock) of the shifting friction element. An engagement-pressure increase rate and an engagement-pressure increase pattern for achieving this differ depending on the driving conditions. If the engagement-pressure increase rate of each shifting friction element is exclusively determined by the degree of flow-rate regulation performed by the orifice or the like as described in Japanese Unexamined Patent Application Publication No. 2004-197758, the demand regarding the selection shock and the demand regarding the selection response, which conflict each other, cannot be satisfied at the same time in a well-balanced manner.
To solve all of the above-described problems, each of the shifting hydraulic circuit for the forward shifting friction element and the shifting hydraulic circuit for the reverse shifting friction element may have a shifting oil-pressure control valve capable of individually controlling the shifting oil pressure (engagement pressure of the shifting friction element) of the shifting hydraulic circuit.
In such a case, the shifting oil pressure of the forward shifting friction element (engagement pressure of the forward shifting friction element) and the shifting oil pressure of the reverse shifting friction element (engagement pressure of the reverse shifting friction element) can be individually controlled.
However, in this case, two oil pressure control valves, that is, a forward-shifting oil-pressure control valve for controlling the forward shifting oil pressure of the forward shifting friction element (engagement pressure of the forward shifting friction element) and a reverse-shifting oil-pressure control valve for controlling the reverse shifting oil pressure of the reverse shifting friction element (engagement pressure of the reverse shifting friction element) are necessary. Because oil-pressure control valves are expensive compared to directional control valves, high costs are incurred.
What is needed is an apparatus that may dampen the pressure when the transmission is switched, shifted, or launched. What is further needed is a single common oil-pressure control valve that may be used as both the forward-shifting oil-pressure control valve and the reverse-shifting oil-pressure control valve, such that a controlled pressure provided by the common oil-pressure control valve may be selectively supplied to the forward shifting friction element or the reverse shifting friction element under distribution control performed by the manual valve.
In such a case, the costs can be reduced because the number of expensive oil-pressure control valves is reduced to one. However, the engagement-pressure reduction rate and the engagement-pressure reduction pattern of the shifting friction elements are constant. In addition, because the oil-pressure control valve starts a pressure adjusting operation after switching of the manual valve is detected, the above-described problems cannot be solved. In addition, when the N→D selection operation or the N→R selection operation is performed, the common oil-pressure control valve supplies the engagement oil pressure (shifting oil pressure) to the forward shifting friction element or the reverse shifting friction element from the state in which the oil pressure is 0. This increases the delay in the engagement response of the shifting friction elements, and a new problem occurs in that the shifting response is degraded.